1. Field of the Invention
The present invention relates to an antenna apparatus provided in a wireless communication device which requires a reduction in thickness (low profile), such as a mobile communication.
2. Description of the Related Art
In recent years, with a reduction in size and weight of electronic communication devices, a reduction in size and weight of electronic components has been demanded. A mobile communication terminal performs most of information propagation by transmission/reception of radio frequency waves. A frequency band of a currently utilized radio frequency is over 100 MHz. Thus, attention has been paid to electronic components and printed circuit boards which are useful in high frequency band such as a giga hertz.
In order to operate with radio frequency waves in such a high frequency band, an energy loss in electronic components must be small. For example, in an antenna apparatus used in a mobile communication terminal, radio frequency waves radiated from an antenna element produce a transmission loss in a propagation process. This transmission loss is transformed as a thermal energy in an electronic component and a printed circuit board to become a factor of heat generation in the electronic component, thereby offsetting radio frequency waves to be transmitted to the outside. Therefore, excessive intensive radio frequency waves more than necessary must be transmitted, and hence there is problem in effective use of the radio waves.
Thus, in a conventional antenna apparatus used in a mobile communication terminal, a distance between an antenna element, an electronic component and a printed circuit board is generally set large size so that radiation characteristics of radio frequency waves radiated from the antenna element are not greatly affected by the electronic component and the printed circuit board.
Further, as another countermeasure, there has been proposed a structure in which a magnetic material plate is arranged on a side opposite to a side where an antenna of a printed circuit board is set, for example (see, e.g., Jpn. Pat. Appln. KOKAI Publication No. 2002-232316).
However, when a distance between the antenna element, the electronic component and the printed circuit board is set large, the antenna apparatus is increased in size. As a result, an antenna apparatus accommodation space in a case of a mobile communication terminal becomes large, whereby an increase in size of the terminal is unavoidable. Furthermore, even if a magnetic material plate is arranged on the side opposite to the side where an antenna of the printed circuit board is set, antenna radiation characteristics are not improved. Therefore, a distance between the antenna element, the electronic component and the printed circuit board must be set large.